This invention relates to drive systems for bicycles and other devices of the type wherein input force is varied during transmittal to a rotary output device to produce an output force of varying magnitude which is variously applied to the rotary output device during each revolution thereof.
This application is related to my prior U.S. Pat. No. 4,133,550, the disclosure of which is specifically incorporated herein by reference.
As disclosed in my prior patent, it is advantageous to provide a drive system for a bicycle, or any other rotary power transmission apparatus, which has input-output force correlation means operably connected to and operable by the crank arm means for correlating input force applied to the crank arm means with output force delivered to the rear wheel, or any other driven device, during the power input cycle while continuously maintaining the application of output force to the rear wheel throughout each power input cycle. In such a system, the apparatus is constructed and arranged for varyingly applying input force during repetitive power input cycles of a rotary or reciprocating input system of a bicycle or the like operatively connected to a rotary output system of a bicycle in which the input system is subject to varying magnitude and direction of application of input force and varying effective resistance of the output system during each power input cycle; varying the magnitude and direction of the transmitted input force during each power input cycle by continuously varying the effective radial and circumferential location of application of the transmitted input force in accordance with the varying effective resistance characteristics encountered by the input system; and continuously maintaining the application of the transmitted input force to the rotary output system throughout each power input cycle. In such a system, maximum transmitted input force may be generated at those circumferential locations of the application of input force to the system at which the effective input force is minimal, or maximum transmitted input force may be generated at those circumferential locations of the application of input force to the input system at which the effective input force is maximal. The variations in magnitude and direction of the transmitted input force are selected in accordance with predetermined desired variations of the input force which may be based upon varying capabilities of bicycle riders. In such a system, the rear wheel position is varied relative to the pedal position during each 360.degree. input force application cycle so that the effective resistance of the rear wheel to rotation is variably transferred to the pedals in a predetermined manner. The amount of input force required to overcome the effective resistance of the rear wheel to rotation at each rear wheel position during each 360.degree. input force application cycle is reduced while varying the rear wheel position relative to the pedal position during each 360.degree. input force application cycle so that the effective resistance of the rear wheel to rotation is variably transferred to the pedals during each 360.degree. input force application cycle in a predetermined manner. The effective resistance of the rear wheel to rotation may be varied in accordance with and relative to pedal position so as to variously match the maximum input force capability of the rider with the resistance to rotation of the rear wheel or to variously match the maximum input force capability of the rider with the maximum effective resistance of the rear wheel to rotation. Such system requires substantially less pedal input force to overcome a given resistance. It may be designed to effect the magnitude of the applied input force relative to output resistance or the magnitude of output torque for a given input force at particular pedal-wheel positions during each revolution.
In general, the drive system of the present invention provides similar results and comprises: input force applying means for applying force to the drive system; rotatable output force transfer means for transferring output force to the rear wheel of the bicycle; mounting means for rotatably mounting said rotatable output force transfer means and enabling rotation thereof relative to the mounting means in both forward and rearward directions; input force transfer means for transferring input force from the input force applying means to the rotatable output force transfer means to cause rotation thereof in the forward direction and transfer of output force to the rear wheel; input-output force correlation means operatively associated with the input force transfer means for correlating input-output forces by forward and rearward relative rotative displacement of the rotatable output force transfer means and the input force transfer means during each revolution of the drive system.
The input-output force correlation means comprises cam means mounted in juxtaposition to and operative relationship with the rotatable output force transfer means and the input force transfer means for controlling the amount and location of the relative rotative displacement therebetween during each revolution of the drive system.
The cam means comprises a cam track having a continuous cam surface extending 360.degree. about the axis of rotation of the rotatable output force transfer means; and cam follower means movably mounted on the cam surface on the cam track for continuous movement therearound during each revolution of the drive system.
The input-output force correlating means further comprises oscillator means operatively connected to the cam follower means and to the rotatable output force transfer means for causing relative rotative displacement of the rotatable output force transfer means. The oscillator means may be pivotally or axially displaceable by the cam means. The oscillator means may be directly connected to the output force transfer means or may be indirectly connected thereto through gear means such as a planetary gear system. An inclined slot means, with a cam driven roller means mounted therein, may be fixedly or adjustedly associated with the output force transfer means for modifying the effect of the cam means on the output force transfer means.
In use as a drive system for a bicycle or the like, the drive system connects the pedal operated crank arms to a rotatable sprocket wheel mounted coaxially with a rotatable crank shaft driven by the pedal operated crank arms. The sprocket wheel is rotatably mounted on the crank shaft which is rotatably supported in the conventional crank shaft housing mounted on the bicycle frame. The cam means is in the form of a plate fixedly mounted on the crank shaft housing circumjacent and axially adjacent one end of the crank shaft so that the cam surface extends thereabout. The oscillator means is mounted between the sprocket wheel and the plate is closely spaced axial relationship therewith. Thus, the drive system of the present invention may be readily adapted for use with other conventional drive system apparatus of otherwise conventional bicycles while providing the advantageous results described herein and in my prior patent.